Terephthalic acid diesters, such as di-n-butyl terephthalate (DBT) and di-isobutyl terephthalate (DiBT), can be used as plasticizers in a variety of polymeric materials such as polyvinyl chloride. However, di-n-butyl terephthalate (DBT) has a melting point of about 16° C. Likewise, pure di-isobutyl terephthalate freezes at an even higher temperature of 54° C. This has led to the concern that these products could freeze when stored at cold temperatures. Freezing of such products often requires installation of heated tanks, transfer lines, and associated handling equipment, thus increasing the cost of using these products. The present invention addresses this concern by producing terephthalic acid diesters having a lowered melting point.